Stereo-video BRUV survey of Rakaumangamanga Rāhui Tapu 2025

Stereo-video ‘BRUV’ survey of Rakaumangamanga Rāhui Tapu 2025

Dr. Adam N. H. Smith
Director, Sea Through Science Ltd

Acknowledgements

Northland Regional Council
- Nicola Hartwell
- Richard Griffiths
Ngāti Kuta and Patukeha hapū
Robert Willoughby
Skipper Bob Clarke, and Eli Sherman, Warren Matene, and Richard Griffiths
Heidi Schlumpf

What is a ‘Stereo BRUV’?

Stereo Baited Remote Underwater Video (SBRUV)
Stainless steel frame with two video cameras pointing at a bait canister, with lights and a depth sensor
Standard method used globally to monitoring fishes

Introducing the stereo baited remote underwater video

Each unit comprises a stainless steel frame with two video cameras, lights, a depth and temperature sensor, and a canister of fresh bait sticking out the front.

We have six of these units, and we throw them into the sea and leave them for just over an hour. The bait attracts fish and other animals, and we can count the organisms and record the habitat.

This has become a standard tool for monitoring fishes internationally. I’ve used these things for several years across New Zealand from the Kermadecs to Fiordland, as well as in several other countries, the Galapagos Islands, New Caledonia, Fiji.

We also used this method in a global study of sharks called Global FinPrint, which surveyed sharks on coral reefs all over the world.

Why stereo? This one of the reasons why this method is so powerful…

What is a ‘Stereo BRUV’?

After calibration with a specialist cube and software,

What is a ‘Stereo BRUV’?

After calibration with a specialist cube and software,
stereo BRUVs allow for accurate measurements of lengths.

The survey

42 deployments in 2 days (contracted to do 36) in May 2025
Four levels of protection

Small snapper and a bronzie

Large snapper

Overall results

Observed 38 species from 22 families of fish
Average of 9.2 species per deployment
Tāmure / snapper were dominant — present at every site, ranging from 15 to 105, average 50
Araara / trevally also very widespread
Sharks and rays included eagle rays, two bronze whalers, short- and long-tail stingrays, and a hammerhead

Results for tāmure / snapper

For raw counts of snapper, rāhui tapu areas are not very different.

But there area clear differences in size and biomass.

Results for tāmure / snapper

Tāmure > 450 cm found only in the area protected since 2010.

Legal-size tāmure found mostly in the rāhui tapu, including newly protected area.

Rapid increase in legal-sized tāmure often observed in no-take areas.

How?

Benefits beyond boundaries

Rāhui tapu are a safe haven for BOFFFs — Big Old Fat Fecund Fish
Estimated seasonal production of eggs (Crossland 1977, 1981)
- 250 mm: 80k–300k
- 500 mm: 4.5M–6M
A source of eggs and larvae for surrounding areas